The episode where Urkel builds an atom bomb and detonates it.
Urkel's voice echoing, as the city is engulfed in a mushroom cloud: Did I do that?!
Steve's imagination sequence where he, dressed as Superman for Halloween, beats up a bank robber.
On the first episode with Myrtle, Steve attempts to serenade Laura with his accordion. Hilarity Ensues.
Rachel: "Well, it's more like Steve's playing caused the neighbors to throw bricks at his house."
In one episode, Eddie dents the car and resorts to illegal gambling with Steve (who never loses) to work up the money to pay for repairs. After he's caught and arrested, Carl gives him a long lecture about fessing up when making a mistake to prevent things from getting out of hand like that. Immediately afterward, Harriet gives Carl the exact same lecture as the second plot of the episode involved Carl accidentally throwing away the cremated ashes of Harriet's recently-deceased great aunt and trying to cover it up.
Urkel: Relax Eddie, there is absolutely nothing that can stop us. Police officer: Freeze! This is a raid! Urkel: Except that.
One episode has Carl and Estelle playing a Mortal Kombat spin-off with an elderly grandma fighting a ninja. Just hearing the "Grandma Wins!" in the deep MK voice makes the whole thing worth it.
Later on Waldo challenges Estelle and initially wins playing as the ninja, until Estelle changes her character to Steve Urkel and makes a comeback.
The three-part Disaster Dominoes building up to Steve and Myra's first kiss, with him making a mess of setting up folding chairs until he throws one into the grill, fumbling around her backyard furniture until he breaks a window, and finally struggling with her hammock.
Richie and 3J are hiding out in the attic and Steve uses an infrared tracking device to find them. However, when he first turns it on, it picks up on Carl.
Harriette: "What's that big blob?"
In the episode "Baker's Dozen", after trying Carl's secret family recipe, Lemon Tarts, Rachael thought of the idea of selling them. Carl thought it's a great idea, until he learns he has to make 12,000 tarts by the coming monday. So everyone (except Harriet) start making the tarts. But after a few hours, they only made several hundreds. Due to the stress of it all, a misunderstanding caused a food fight between Carl and Rachael. Rachael accidentally threw flour at Laura, who then tries to get back at her with more flour. Eddie yells "food fight!" and starts throwing some tarts at Carl, then he throws some back. It escalates, until they were interrupted by Urkel, who asked if there's anything to eat. Everyone throws some tarts at him before resuming their fight. When Harriet shows up to stop them...
In "The Party", where Carl, Harriet, Rachel, and Carl's mother are on their way to Sheboygan.
After waiting for the tow truck for so long:
Carl: I don't get it! I specifically told him we're by the 180 sign! Harriet:(wipes the snow from the sign) Carl, the sign has 130! Carl:(takes a look) Didn't I say 130? Harriet: No! You said 180! Carl: That explains the delay. Please don't tell Rachel and mama. Harriet: Fine! Let's just get inside the car! (after getting in) Rachel: Well, what's going on? Harriet: Carl got the sign wrong. We're back to square one. Carl: They had to beat that out of you didn't they?
The highway patrol officer arrives:
Officer: What seems to be the problem? Carl: We have some car trouble. Officer: Where are you folks heading? Carl: We're on our way to Sheboygan. Officer: On this road? Nobody takes this road to Sheboygan. (Harriet, Rachel, and Carl's mom glare at him) Carl:(laughing nervously) See Harriet? I'm the only one who knows this shortcut.
Carl's stress relief mantra from a cheap brochure:
Carl: Three-two-one...one-two-three...what the heck is bothering me?
Then he gets fed up with giving Steve driving lessons and finds the answer to the question...
Carl: Three-two-ONE! One-two-THREE! What the HECK is bothering ME?!?.........YOU!!!
Steve and Laura come home from bowling and Steve's wearing a kilt and has a bowling ball stuck on his toe and he zipped his bowling bag over his foot as well because he didn't want to look ridiculous.
Laura: First he put on that stupid kilt. Then he made a stupid bet that he could bowl a stupid strike with his stupid foot. Then he got his stupid TOE caught in the stupid ball!
Steve: Well, it could have happened to anyone.
Laura: Oh, don't be stupid!
Carl's nightmare from the same episode where he dreams he's in the future and that Steve and Laura got married and had lots of mini Urkels (with another on the way)
"STEVE URKEL IS ENTERING THE MALL!!!"
The sequence in "It's Beginning to Look a Lot Like Urkel", where Laura's guardian angel switches Steve and her's lives so they become Steve Winslow and Laura Urkel. This leads to Carl and Harriet's roles being reversed as Harriet is the one who tries to hurt Laura after she destroys Harriet's gingerbread house:
Laura Urkel Did I do that?
Harriet Yeah. And I'm 'bout to do this COME HERE! (lunges at her, Carl and Eddie hold her back)
The episode "Citizen's Court" had plenty of this. Not surprising, considering it was about Steve suing Carl after the latter killed his Peruvian stick bug. Of particular note are Carl's reaction to finding said bug on his chest during a nap, Steve's pronunciation of "bric-a-brac," and Eddie's testimony about his hamster, Mr. Fluffkins.
In one episode, Eddie blames behavior at school on a bad home life. His teacher visits the home and finds the following: Ritchie is literally making meals out of junk food note Rachel is teaching him a lesson' Estelle is talking about buying men note it's a bachelor auction; and Carl is demanding where some clothing is so he can wear it to buy drugs note he's an undercover cop. The entire scene and the reaction of the teacher (who doesn't know the context of any of this) is priceless.